Throughout the disclosure and claims, we will be using the term MPEG (Motion Pictures Expert Group). MPEG is a generic reference to a family of international standards, which define how to encode visual and audio information in a digital compressed format.
MPEG is utilized in a wide variety of applications, including: DVD (Digital Video Discs) and satellite transmission of television signals.
The MPEG standards specify exactly the format in which the compressed data is to be transmitted. A key feature of MPEG is that it can compress a video signal into a fraction of its original size. MPEG achieves a high compression for video by storing only the changes from one video frame to another, instead of each entire frame.
There are two major MPEG standards: MPEG-1 and MPEG-2. The most common implementations of the MPEG-1 standard provide video quality slightly below the quality of conventional VCR (Video Cassette Recorder) videos. MPEG-2 provides higher resolution, with full CD quality audio. This is sufficient for the major TV standards, including NTSC (National Standards Television Committee) and HDTV (High Definition Television). MPEG-2 is used by DVD.
As the use of MPEG increases, there has become a need to identify the original provider of an MPEG transmission. The ability to identify the provider is necessary to determine non-authorised use or dissemination of the content in an MPEG transmission. The owner of a digital transmission often wants to know if their transmission has been copied. The attempt to uniquely identify or “fingerprint” a digital transmission has resulted in the following U.S. patents.
U.S. Pat. No. 5,960,081 discloses the concept of “adding an imperceptible or barely visible signature or a watermark to the images”. It is clear from the disclosure that the inventors are not certain that the embedding of a signature will not affect the quality of the image (column 13, line 18). As the signature is part of the image it may not always be reliably retrieved, thus the inventors repeatedly code the signature in multiple images, resulting in redundancy and increased bandwidth. The inventors go to great lengths to determine which portion of an image is optimal to contain a signature. This solution is compute intensive, as demonstrated by the use of a massively parallel CRAY computer for the tests cited in the disclosure.
U.S. Pat. No. 6,005,643 discloses a method and system of embedding extra information into the frames of an MPEG video stream. This extra information provides a fingerprint or signature. Multiple algorithms are employed to: determine which frames should contain the new data, avoid loss of image quality and to decode the extra information. This invention requires complex algorithms be implemented in both encoder and decoder. Further, the invention requires modifying image frames to encode the required extra information. In doing so, such a solution must ensure that image quality is not degraded, which is not a simple problem for any algorithm and often easily detected by a viewer.
U.S. Pat. No. 6,009,176 discloses a method of encoding a digital signature in the user data section in the MPEG video elementary stream. Information stored in a first block is encrypted and placed in the next block and the process continues, with each block containing encrypted data based upon the data in the previous block. This solution requires that a decoder be able to read and decrypt each block in real time and determine if it is from the original source. This provides a real time solution to the verification of an MPEG transmission but requires that the decoder decrypt and verify each block before allowing it to be presented to a user.
U.S. Pat. No. 6,047,374 discloses a method of embedding an “authentication stamp” (column 6, line 4) within a digital block. This stamp can comprise any type of data embedded in any type of digital data stream. The algorithm for embedding is left to the reader, but the intent is to embed some form of “meta-data” (column 2, line 66) along with a signature of some form. It is clearly the intent of the inventor that the stamp be embedded directly in an image and the inventor recognizes the flaws in this process. In claim 1 (column 11, line 48,49) he states “so that said bit string is not readily noticeable”. As with other prior art, the embedding of signature information within an image does corrupt the image and may make the change visible to a person viewing the image.
U.S. Pat. No. 6,064,748 discloses a method and apparatus for embedding “an additional data bitstream” into the high level headers of an MPEG data stream. Suggested headers are: video sequence header, group of pictures header or picture header. As the headers are not scrambled in an MPEG transmission, this data may be easily extracted. The invention requires that the order of the frames in the data stream be preselected to create a desired bitstream, which would contain the desired signature (column 5, lines 54, 55). This requirement for preselection of frames may result in a less than optimal transmission as confirmed by the inventors (column 4, lines 39–44).
U.S. Pat. No. 6,069,914 discloses a spread spectrum method for inserting and extracting watermarks in video images. The watermarks are created by applying a discrete cosine transform (DCT) to a plurality of 8×8 pixel blocks of an image. A single pseudo random number is inserted into the DCT coefficient of the spectral shaping algorithm for each 8×8 block. The embedding of a watermark does corrupt the image and may make the change visible to a person viewing the image.
There is thus a need for a simple solution to trace the source of an MPEG stream. Such a solution would:                a) imbed a digital signature in the content;        b) not require significant computing resources as usage increases;        c) place the signature in pre-compressed MPEG content;        d) be sufficient for post mortem identification of an MPEG stream; and        e) be sufficiently hidden to protect the removal of the signature.        
The present invention addresses this need.